1. Field of the Invention
The present invention relates to a lithium rechargeable battery, and more particularly, to a lithium rechargeable battery having a multidirectional lead-tab structure.
2. Related Art
A rechargeable battery is classified according to a structure form of an electrode assembly having a positive electrode/separator/negative electrode structure and includes a jelly-roll (winding type) electrode assembly of a structure in which long sheet type positive electrodes and negative electrodes are wound with a separator interposed therebetween, a stack type electrode assembly of a structure in which a plurality of positive electrodes and negative electrodes cut in a predetermined size are sequentially stacked with a separator interposed therebetween, and a stack/folding type electrode assembly of a structure that winds bi-cells or full cells in which a predetermined unit of positive electrodes and negative electrodes are stacked with a separator interposed therebetween.
Nowadays, interest has increased in a pouch type battery of a structure in which a stack type electrode assembly or a stack/folding type electrode assembly is housed in a pouch type battery case of an aluminum laminate sheet due to a low production cost, a small weight, and easy form modification, and use of the pouch type battery gradually increases.
FIG. 1 is an exploded perspective view illustrating a conventional typical pouch type rechargeable battery.
Referring to FIG. 1, a pouch type rechargeable battery 10 includes an electrode assembly 30, electrode tabs 31 and 32 extended from the electrode assembly 30, electrode leads 40 and 41 welded to the electrode tabs 31 and 32, and a battery case 20 for housing the electrode assembly 30.
The electrode assembly 30 is a power generation element in which a positive electrode and a negative electrode are sequentially stacked with a separator interposed therebetween and is formed in a stack type structure or a stack/folding type structure. The electrode tabs 31 and 32 are extended from each electrode plate of the electrode assembly 30, and the electrode leads 40 and 41 are electrically connected by, for example, welding to a plurality of electrode tabs 31 and 32, respectively, extended from each electrode plate, and a part thereof is exposed to the outside of the battery case 20. Further, in order to secure an electrical insulation state while increasing a sealing degree with the battery case 20, an insulation film 50 is attached to a part of an upper surface and a lower surface of the electrode leads 40 and 41.
The battery case 20 includes a case body 22 including a concave shape of reception portion 23 for receiving the electrode assembly 30 and a cover 21 that is integrally connected to the case body 22, and in a state where the electrode assembly 30 is received in the reception portion 23, by bonding an upper end portion 25 and a both side portion 24, which are contact portions, a battery is complete. Because the battery case 20 is formed in an aluminum laminate structure of a resin layer/metal thin layer/resin layer, by applying a heat and a pressure to the upper end portion 25 and the both side portion 24 of the contacting cover 21 and case body 22, a resin layer is fused and bonds them. Because the same resin layer of the upper and lower battery case 20 directly contacts, the both side portion 24 can be uniformly sealed by melting. However, because the electrode leads 40 and 41 are protruded from the upper end portion 25, in order to improve a sealing property in consideration of a thickness of the electrode leads 40 and 41 and a material of the electrode leads 40 and 41 different from that of the battery case 20, by performing thermal fusion with an insulation film 50 interposed between the electrode leads 40 and 41, a battery is finally manufactured.
FIG. 2 is an example of another pouch type battery and is a perspective view illustrating a pouch type battery in which an electrode lead is protruded from each of an upper part and a lower part of a battery case.
A pouch type battery 101 of FIG. 2 is different from the pouch type battery of FIG. 1 in that electrode leads 411 and 421 are positioned at an upper part and a lower part, respectively and a battery case is separated as a lower case 221 and an upper case 231. Therefore, in the battery case, the lower case 221 and the upper case 231 are bonded by thermo-compression and an upper sealing portion 241, a lower sealing portion 261, and both side surface sealing portions 251 and 271 are formed. A reception portion 211 may be formed only in the upper case 231 or the lower case 221, or in both the upper case 231 and the lower case 221.
As shown in FIGS. 1 and 2, in a conventional battery, after electrode plates are stacked so that tabs of the same polarity are aligned at the same position in an axial direction, by welding tabs of the same polarity with one positive electrode or one negative electrode, a battery is manufactured.
A battery manufactured in this way may be used as a battery of a small capacity use, but when a battery manufactured in this way is used as a medium and large battery use using a large current, a problem may occur. That is, when the battery is used for use requiring much energy, such as a vehicle, as a magnitude of a current passing through a lead increases, much heat generates and thus a problem may occur from a safety point of view.
In order to solve such a problem, a method of increasing a thickness or a width of a lead-tab may be used, but in this case, a sealing property of a lead-tab portion may be not good and thus a problem that moisture penetrates into the portion may occur. Further, because a lead and a tab having no standard size are used in a mass production process, difficulty may arise in a production process.
Therefore, a demand for a battery appropriate for using a high current even while using a conventional lead-tab size has been increased.